Definition: index

(1) See indexed color.

(2) A common method for keeping track of data so that it can be accessed quickly. Like an index in a book, it is a list in which each entry contains the name of the item and its location. However, computer-based indexes may point to a physical location on a disk or to a logical location that points elsewhere to the actual location.

Indexes are used by all types of software, including the operating system, database management system (DBMS) and applications. For example, the file system index in an operating system contains an entry for each file name and the starting location of the file on disk. A database index has an entry for each key field (account number, name, etc.) and the location of the record. Search engines use a very sophisticated indexing system to keep track of billions of pages on the Web.

(3) In programming, a method for accessing data in a table. See subscript and inverted file.

Types of Indexes

Indexes are widely used to keep track of the physical location of files on the disk as well as the logical location of data within a database. On the other hand, a programming index is a counter that is incremented to point to a relative location in a table.